Flake said the new tariffs, which function as taxes on imports, of 25% on steel and 10% on aluminum would be detrimental to the US economy and must be stopped.

"These so-called 'flexible tariffs' are a marriage of two lethal poisons to economic growth – protectionism and uncertainty," Flake said in a statement. "Trade wars are not won, they are only lost."

A slew of Republicans, including House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, expressed concern about the tariffs in the run up to the announcement. Trump ultimately backed down slightly from what were initially described as broad-reaching, indiscriminate tariffs, exempting Canada and Mexico as well as creating a pathway to exemption for other nations.

But Flake said that was not enough and Congress must act.

"Congress cannot be complicit as the administration courts economic disaster," the Arizona senator said. "I will immediately draft and introduce legislation to nullify these tariffs, and I urge my colleagues to pass it before this exercise in protectionism inflicts any more damage on the economy."

While Republicans came out against the trade measure, Flake is the first to announce a legislative response.

Flake has been a vocal critic of the president. He is set to retire after 2018.